fix: JSON Collection Unwrapping Consistency in Programmatic Interface

[Shiva953]

This pull request addresses an inconsistency in the programmatic interface of Newman related to the handling of JSON collections as described in #3179. When a collection is passed directly as JSON, there was unexpected behaviour compared to loading it from an external file, especially when unwrapping was required.

Changes Made:

• Modified the extractModel function in newman/lib/run/options.js to ensure consistent unwrapping behaviour for JSON collections.
• Added checks for the presence of the "values" property to distinguish between variables and other objects.

[Shiva953]

would love a review for this, @codenirvana